Unless otherwise indicated herein, the description in this section is not prior art to the claims and is not admitted to be prior art by inclusion in this section.
A typical cellular wireless network includes a number of base stations each radiating to define a respective coverage area in which user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices (whether or not operated by a human user), can operate. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the network may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Further, a cellular wireless network may operate in accordance with a particular air interface protocol or “radio access technology,” with communications from the base stations to mobile terminals defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Wireless Interoperability for Microwave Access (WiMAX), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of mobile terminals, initiation of communications, handover between coverage areas, and other functions related to air interface communication.
In accordance with the air interface protocol, each coverage area may operate on one or more carrier frequencies or range of carrier frequencies. Further, each coverage area may define a number of channels or specific resources for carrying signals and information between the base station and UEs. For instance, certain resources on the downlink may be reserved to carry a pilot or reference signal that UEs may detect as an indication of coverage and may measure to evaluate coverage quality. Further, certain resources on the uplink may be reserved to carry access requests from UEs seeking to gain access to the base station. And certain resources on the downlink may be reserved to carry control messaging such as paging messages and random access response messages from the base station. In addition, certain resources on the uplink and downlink may be set aside to carry bearer traffic (e.g., user communications) in a manner assigned or scheduled by the station for instance.
When a UE is within coverage of a base station, the UE may from time to time transmit to the base station an access request message. The purpose of such an access request message may depend on the air interface protocol and the circumstances. By way of example, a UE may transmit an access request as a request to gain initial access to communicate with a base station, such as to transition from an idle state to a connected state for instance, or to facilitate handover to the base station. As another example, a UE may transmit an access request as a response to a paging message and/or as a request to establish a particular communication connection such as a call or data session. And as still another example, a UE may transmit an access request to register or reregister with a base station and/or to provide a location or tracking area update. Once the base station receives a UE's access request, perhaps after further processing by the base station and/or associated infrastructure, the base station may then transmit an access response message to the mobile terminal.
By way of example, an access request that a UE transmits to a base station may comprise a preamble that takes the form of a signature or pattern randomly selected from a plurality of preambles. For instance, in an LTE system, 64 such preambles are available, and the UE may randomly select one of the preambles to transmit to the base station on an uplink random access channel (RACH). Since multiple UEs may be transmitting access requests at the same time, the preamble may serve to differentiate the access request transmitted by the UE from other access requests transmitted by other UEs.
In LTE, a UE's preamble transmission does not identify the UE but rather serves to notify the base station generally that a UE is trying to gain access. In response to receiving such a preamble, the base station then transmits a random access response for receipt by whichever UE happened to have sent the preamble (associating the response with the transmitted preamble and/or with associated timing or other attributes, to enable the UE at issue to receive the response to its access request), and the random access response provides that UE with a temporary identifier (T-CRNTI) and an initial assignment of uplink shared channel (PUSCH) resources on which the UE can then transmit a request for a radio-link-layer connection with the base station. Thus, upon receiving that initial assignment of uplink resources, the UE then uses the initial PUCH resource allocation to transmit to the base station a radio-link-layer connection request (Radio Resource Configuration (RRC) Connection request) that carries the provided temporary identifier so that the base station can associate the request with the access-process underway, and that carries the UE's actual identifier so as to inform the base station which particular UE is actually making the access request. And in response, the base station then assigns to the UE a full identifier (C-RNTI) for a radio-link-layer connection between the UE and base station, so that the UE can then engage in further air interface communication with the base station via that radio-link-layer connection.